Wooden roof trusses comprise various pieces of dimensional lumber members typically held together at the intersections of the members by metal nail or connector plates to form a rigid structure. The metal nail plates are formed with a multiple number of teeth. The wooden members are held in the truss configuration by a jig that allows nail plates to be placed at the intersections of the wooden members. Nail plates are placed on both sides of the truss members at the intersection so as to form a rigid adjoinment when the nail plates are pressed into the wooden members.
Most trusses are fabricated either in a retaining jig laid out on a table serving as a work surface or on stands that are positionable over the work surface area. The table method utilizes a jig laid out on a table two to three feet above the floor. When the stand method is used, the stands are positioned at the intersections of the truss members to support the truss members and form the jig. The stands are at a similar height to the table.
When pressing stands are used, two general methods are used for positioning the stands. One method uses a smooth floor as a work surface so that the pressing stands can be easily moved around to desired positions. The floor may be covered with a steel sheet to allow securing of the pressing stands at desired locations with magnetic clamps. The other stand method uses a set (two) of base rails on a work surface with a number of sets of paired rails (branch rails) placed at ninety degrees to and extending from the base rails. Pressing stands are slidably mounted on the base rails. Pressing stands are also slidably mounted on the branch rails. The branch rails are slidably attached to the base rail. By positioning both the branch rails relative to the base rails and the stands on the base and branch rails, the stands can be located at the joints of a truss to be formed. Neither method of construction lends itself to precision placement of the pressing stands.
Where pressing stands are used, an hydraulic press formed in the shape of the letter "C" is used to press the connector plates into the wooden members. It is generally known as a C-clamp press. For trusses laid out on a table a roller press or gantry press is typically used.
In both the table and stand methods, the initial truss members must be used to finally position the jigs or stands holding the truss components before applying the connector plates. This is done after the jigs or stands are roughly positioned at the joints of the truss to be formed, typically using a tape measure. After the initial truss components are placed in the jig or on the stands, critical dimensions must be checked, such as height and span of the truss. Final adjustments of the positions of the jigs or stands are then made so that they coincide as precisely as possible with the intersections of the wooden members and the locations where the connector plates will be applied. When the initial truss components are used to set up the jig or stands, the jig or stands cannot be set up in their final locations until the truss components have been cut and brought to the press location.
The setup processes described are time consuming, labor intensive, and imprecise. Additionally, the table method of building trusses has the disadvantage of requiring that the workmen get up on the table and work in a crouched or bent over position. A higher incidence of back trouble results from the use of the table method of truss construction as compared to the stand method.
U.S. Pat. No. 4,943,038 to Harnden teaches the use of lead screws to position jig stops on a plurality of table sections in a table method of assembly. However, the method of this patent still requires that the initial truss be used to set up the jig stops and also requires that a worker place the truss components in place on the table prior to the press setup.
U.S. Pat. No. 4,754,910 to Rehn discloses a modified pressing stand method and apparatus for fabricating a roof truss. However, such method would appear still to require final positioning of the pressing stands along their guideways after the initial truss members are supported on the stands. Such method also provides no apparent method of accurately and quickly positioning the stands during the initial setup without the aid of manual measuring means.